The Elfin Child - Philip G Bell

This is a children's fantasy story that follows a boy recovering from illness in the city and sent to the country to stay with his Aunt during the school holidays. Whilst playing in a nearby wood, he meets an Elfin boy of the same age. Although initially wary, he eventually allows himself to be drawn into a parallel world, full of strange creatures. He also discovers that prophecies foretold that he would save this world from a dire fate. The book was originally written for children from around the age of 9 years and up, but has proved popular with teens and adults.